Synthetic Polyesters

Besides the work on natural PHA-polyesters, degradation experiments in seawater with synthetic polymers such as poly(e-caprolactone) (PCL) and modified polyethylene (PE) are also reported in the literature. 

Polyolefins such as PE and polypropylene (PP) are usually not accessible to direct microbial attack. For such polymers, biological degradability is achieved hy the addition of starch, prooxidant additives or photosensitive components. Starch, a natural polymer, can he degraded by microorganisms which enhances the defragmentation of the polyolefins (if the starch is accessible to the microbes). The additives increase the initial reduction of polymer chain length by chemical 

However, no significant changes in material properties nor any reliable weight loss of differently modified PE and PP could be observed by Gonsalves and co-workers [9, 10] upon exposure to seawater (1-9 m depth, temperatures of 13-30 °C) for 5-12 weeks. The primary (chemical) degradation depends on the exposure temperature and the normal temperatures (maximum and minimum) found in seawater, the reaction rate is probably too slow to observe any changes in the materials within the duration employed. 

Recent studies show that compostable carrier bags can undergo a strong physical degradation when exposed in the open sea [13]. Degradation is not just due to a mechanical effect, but it is the consequence of true biodegradation as shown by [14] in a study where the marine environment is subdivided into its different habitats and a specific test method is proposed or required for each habitat. 

Originally developed by Carothers in 1932, polylaetie aeid is making a eome-back on the commercial scale. Poly(lactic aeid) (PLA) is a linear aliphatie polyester based on lactic acid which can be produeed via biological (fermentation of starch) or chemical methods. Lactic acid has both hydroxyl and carboxyl 

Polylactic acid is a popular material in various biomedical applications, such as dmg delivery, sutures and orthopedic devices. In the body, PLA is hydrolyzed to its monomeric form, lactic acid, which is then eliminated by incorporation into the Kreb s cycle. Cargill-Dow LLC is producing PLA to the tune of 140kt annually in Blair, Nebraska, USA. Their primary application is the production of fibers through melt-spinning for clothing. Other applications include food packaging such as thermoformed containers and pop bottles. The monomer, lactic acid, has the potential to become a new bio-based material from which other chemicals (acrylic acid, propylene oxide, ethyl lactate) can be synthesized. 

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In order to develop a tissue-engineered heart valve, a group at Children s Hospital in Boston evaluated several synthetic absorbable polyesters as potential scaffolding materials for heart valves. Unfoitu-nately, the most synthetic polyesters proved to be too stiff to be function as flexible leaflets inside a tri-leaflet valve. " In the late 1990s, a much more flexible PHAs called poly-3-hydroxyoctanoate-co-3-hydroxyhexanoate (PHO) was used as the scaffold material for the valve leaflet, and then the entire heart valve. ... 

When polyester-hydrolyzing activity was isolated using synthetic polyesters such as polycaprolactone, and the enzyme was examined in detail, it was found that it was a cutinase that was responsible for the hydrolysis [113]. Similarly, the polyester domains of suberin were found to be degraded by cutinase. Cutinase is a polyesterase, and similar enzymes may be widely distributed and can degrade a variety of natural and synthetic polyesters. Microbial polyhydroxy-alkanoic acids that are attracting increasing attention as biodegradable polyesters can be hydrolyzed by bacterial polyesterases that share some common features with cutinases [114] and this area is covered in another chapter [115]. 

Also displayed in Table II are spin-lattice relaxation data for liquidlike (CH2) groups that were observable in DPMAS experiments. Both the dependence on temperature and the particular Ti values suggested rapid segmental motions within long runs of methylene groups, quite similar to the dynamic behavior reported for soft-segment CH2 s in synthetic polyesters (19). 

Aliphatic polyesters are the most economically competitive of the biodegradable polymers moreover, synthetic polyesters are expected to be degraded nonspecifi-cally by lipases. Although these polyesters are biodegradable, they often lack good thermal and mechanical properties. On the other hand, aromatic polyesters - such as... 

Mueller RJ (2006) Biological degradation of synthetic polyesters - enzymes as potential catalysts for polyester recycling. Process Biochem 41 2124-2128... 

Solvent dyes are dyes that are soluble in alcohols, chlorinated hydrocarbon solvents, or liquid ammonia, and there appears to be considerable promise in dyeing the difficult-to-dye synthetics, polyesters, polyacrylates, and triacetates, from such solutions. 

Like amides, esters are common both in nature and in the chemical industry. Animal fats and vegetable oils are mixtures of esters, as are waxy materials such as beeswax and spermaceti. Plants often synthesize esters that give the characteristic tastes and odors to their fruits and flowers. In addition to making synthetic esters for flavors, odors, and lubricants, chemists have made synthetic polyesters such as Dacron polyester fiber used in clothing and Mylar polyester film used in magnetic recording tapes. 

Polyester is a general term referring to any polymer where the monomers are linked by ester bonds and includes the biodegradable microbially derived polyhydroxyalkanoates, which, as they are naturally produced, are beyond the scope of this article (for a review see Kim Rhee, 2003). Most synthetic polyesters in large-scale use are the aromatic poly(ethylene tetraphthalate) or poly(butylene tetraphthalate) polyesters as they have excellent material properties and are used in a wide range of applications including plastic containers, fibres for synthetic fabrics, films... 

Scherer, T. M., Fuller, R. C., Lenz, R. W. Goodwin, S. (1999). Hydrolase activity of an extracellular depolymerase from Aspergillus fumigatus with bacterial and synthetic polyesters. Polymer Degradation and Stability, 64, 267-75. 

C0-p-C6H4-C00CH2CLt20)n-, a synthetic polyester prepared by esterification of terephthalic acid with methanol and subsequent polycondensation of the ester with ethylene glycol. 

It is important to recognize that all polymers, be they natural or synthetic, are simply giant long chain molecules or macromolecules. It s all chemistry, and there really is no basic difference between a natural or synthetic polymer, in that both obey the same physical laws. Cellulose, for example, the natural polymer that is found in cotton and numerous other plants (and the most abundant polymer on the face of the planet), is a long chain macromolecule composed of carbon, hydrogen and oxygen. So is the synthetic polyester fiber, polyethylene tere-phthalate) (PET). It s just that the arrangement (architecture) of the atoms in the two... 

The concept of polymeric soil release agents has been around for well over 25 years. The initial polymer chemistries (polyethylene terephthalate-polyoxyethylene terephthalate, PET-POET) were designed to deposit on fabrics and facilitate oily soil removal upon subsequent washing [98,133,134], The limitation of this chemistry was its effectiveness on synthetics (polyester) alone, with limited benefits being observed on cotton and synthetic blends. In recent years the focus has shifted to delivering soil release on cotton. Two classes of polymer chemistries have been disclosed in the recent patent literature for cotton soil release one based on hydrophobically modified polycarboxylates derived from acrylic acid and hydrophobic comonomers at defined molar ratios [188] and the other based on modified polyamines [189-193],... 

At the time of writing, the applications of biodegradable polymers are confined mostly to the field of agriculture, where they are used in products with limited lifetimes, such as mulch films and pellets for the controlled release of herbicides. The synthetic polyesters used in medical applications, principally polylactide and poly(lactide-co-glycolide), while claimed to be biodegradable, are degraded in the body mainly, if not entirely, by chemical hydrolysis. There is little evidence that the hydrolysis of these polyesters of a-hydroxyacids can be catalyzed by hydrolase or depolymerase enzymes. 

Thickness is for fluoropolymers only. For glass backing add 35 milli-inches and for synthetic (polyester) add 15 milli-inches. To convert from milli-inches to mm, multiply by 0.0254. ... 

Polytetrafluoroethene -PTFE, etc. (Back spinning) synthetic polyester... 

Birkimer D. L., and Lindeman, R. A., Dynamic Tensile Strength of Synthetic Polyester Concrete, ASCE National Structural Engineering Meeting, Meeting Preprint, American Society of Civil Engineers, New York, 1157 1-12 (1970)... 

DIN 53183 defines an alkyd resin as follows Alkyd resins are synthetic polyester resins produced by esterifying polyhydric alcohols with polybasic carboxylic acids. At least one of the alcohols must be trihydric or higher. Alkyd resins are always modified with natural fatty acids or oils and/or synthetic fatty acids. In order to obtain particular application technology properties, alkyd resins may be additionally modified with compounds such as resin acids, benzoic acid, styrene, vinyltoluene, isocyanates, acrylic, epoxy, or silicone compounds. ... 

Terephthalic acid finds extensive application in the manufacture of synthetic polyester-type fibers (notably Dacron and Teiylene). Commercially, it is produced by the liquid phase oxidation of /j-xylene. Thermal disproportionation of the potassium salt of benzene carboxylic acid (obtained from benzene) in the presence of cadmium as a catalyst, followed by hydrolysis of the potassium terephthalate, is another potentially attractive route. 

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